v0.5.0

ETag conditional-revalidation cache — the only thesis-safe way to be faster without becoming a stale index. An ETagCachingHTTPClient decorator wraps the network layer: when a URL is cached it always re-requests with If-None-Match, so the server decides freshness. On 304 Not Modified it serves the cached body (no re-download/re-parse of an unchanged, often large doc like an llms.txt); on 200 with a new ETag it refreshes. It deliberately ignores max-age — "latest" stays latest, it's just cheaper when nothing changed. Sources without an ETag (e.g. some registry endpoints) are simply not cached; POSTs (GraphQL introspection) are never cached. In-memory, per session.